Sliding thin film resistance for measuring instruments

ABSTRACT

A variable resistor is provided wherein a thin metallic film is deposited as by sputtering on a base of insulating material. The thin film consists of at least two layers; the bottom layer being of a base metal selected from the group consisting of manganese, titanium beryllium, tantalum, nickel and chrome, or alloys thereof, and the upper layer being of palladium.

United States Patent [72] Inventor Yutah Wlteno 3,252,831 5/1966 Ragan Q 117/227 X Tokyo, Japan 3,274,022 9/1966 Rhoda.. 117/227 X [21] Appl. No. 768,716 3,415,679 12/1968 Chuss... 117/217 X 1 Flled 1968 2,734,976 2/1956 Strege 338/196X [45] Patented 0621, 1 3,106,489 10/1963 Leaselter 29/195 UX 8 pp 8 3,290,127 12/1966 Kahng et al...... 29/195 e 1 11 3,339,267 9/1967 Bronnes 6151... 29/195 x [32] Priority Oct-24,1967 3,353,134 11/1967 Elarde 338/308 x hi 3,458,847 7/1969 Watts 338/308 x 42/6803! 3,495,959 2/1970 J0hnson,Jr 29/195 1 OTHER REFERENCES [54] SLIDING THIN FILM RESISTANCE FOR W. H. Nebergall, F. C. Schmidt, H. F. Holtzclaw, .lr.,

I MEASURING INSTRUMENTS General Chemistry D. C. Heath & Co., Boston, 1963, p. 706

2 Claims 3 Drum! Figs Primary Examiner-Alfred L. Leavitt [52] U.S.Cl 338/140, Assistant Ex min r-C. K- W iff n h 117/217, 117/212, 117/221, 117/227, 338/142 Mummy-Anton 1 wine [51] Int-Cl l-l0lc 5/06 29/195;

W212, 217 221 227; 33 30 309 19 200 ABSTRACT: A variable resistor is pl'OVldCd wherein a thln 185 186, 190, 194, 140 142 metallic film is deposited as by sputtering on a base of insulating material. The thin film consists of at least two layers; the [56] References Cited bottom layer being of a base metal selected from the group UNITED STATES PATENTS consisting of manganese, titanium beryllium, tantalum, nickel 2,632,831 3/1953 Pritikin etal. 338/140 "'3 :l '9" the upper layer bemg 2,897,584 8/1959 Schumpelt 117/21-7 ux, a

7 6 4' 3 1 .1 I 1 ,5 ,1 k 9 F 7 g I: 4; .J: IJQ Q 71/- -7 7'1 L L 4 Q Z A PATENTED 051221 m1 FIG.

FIG.2

SLIDING TIIIN FILM RESISTANCE FOR MEASURING INSTRUMENTS This invention relates to a variable resistor in which a thin film having electrical resistive characteristics is deposited on a baseplate of insulating material, a sliding contact engaging the deposited film. The variable resistor is particularly useful for measuring instruments such as exposure meters.

In conventional resistor units for measuring instruments, and the like, the resistance elements are formed of a carbon film, a nickel-chrome alloy film, or a chrome-gold double layer film.

With the conventional carbon film, the resistance value of the elements changed considerably with use and wear. The nickel-chrome elements had similar drawbacks, the resistance value changing in various positions of the sliding contact as abrasion took place with use.

It was found that by increasing the pressure of the sliding contact that the differences in the resistance values thus obtained from those values obtained by sliding the contact over the nickel-chrome elements could be reduced, but this increase in contact pressure also increased the abrasion of the elements. The chrome-gold resistance elements where the gold film formed the upper layer, the same difficulties due to wear are also encountered.

ln measuring instruments such as an exposure meter used for photography, a carbon film resistor is used for the most part, a nickel-chrome film'element being used in conjunction therewith as a film-sensitivity-adjusting element. In such instruments, the variable resistors are quite small and very little force is available for moving the sliding contact. It is thus desirable to have a variable resistor in which the resistance element surface has a high wear resistance and in which very little pressure is required to engage the sliding contact with the resistance element and in which a very small force is required to move the sliding contact so that stability of the resistance values is obtained.

The object of the present invention is to provide a variable resistor for measuring instruments wherein a small force is required to move the sliding contact, the sliding contact firmly engaging the resistance element or elements with a slight pressure, and wherein the resistance element or elements comprising a thin film has a high resistance to abrasion.

In accordance with the present invention,a variable resistor for measuring instruments is provided wherein a thin film of electrical resistive characteristics are deposited on a baseplate of insulating material, the thin film comprising of at least two layers; the lower layer being of a base metal selected from the group consisting of manganese, titanium, beryllium, tantalum, nickel and chrome, or alloys thereof, the upper layer being of palladium and engaged by the sliding contact.

This invention will be described more clearly referring to the illustrative embodiments shown in the attached drawings, in which:

FIG. 1 is a plan view of an embodiment of this invention;

FIG. 2 is a side view thereof; and

FIG. 3 is a plan view of another embodiment of this invention.

Referring to FIGS. 1 and 2 of the drawing in which one embodiment of the invention is illustrated, the variable resistor comprises a baseplate 1 of insulating material having deposited thereon a film 2 of electrical resistive material. Provided at one end of the triangular shaped film 2 is an electrode 3 serving as an electrical connection for the variable resistor. A sliding contact 4 is provided for engaging the surface of the film 2, the contact being movably (by means not shown) along a straight line from the apex of the triangular film to the electrode 3. The film 2 is in two layers, the lower layer being in this instance chrome and the upper layer being palladium. The sliding contact 4 is preferably made of phosphor bronze wire about 0.3 mm. in diameter and engages the palladium layer with a pressure of several grams. The triangular shape of the film 2 provides a functional change in the resistance values as the sliding contact is moved along its straight line path between the apex and base of the film.

The film 2 as previously mentioned is a double-layer film of chrome and palladium. The chrome layer is deposited first on the baseplate l and may be deposited by sputtering or any other well-known process. The palladium layer is similarly deposited on the chrome layer. It has been found that palladium is not subject to changes in resistivity when the sliding contact is being moved over or remains stationary on a particular position regardless of the material comprising the sliding contact and even though only slight contact pressure is applied. Palladium also has excellent wear resistance to that there is very little change in the resistance values obtainable even after many movements of the sliding contact. When the thickness of chrome film is from A. to I000 A. and the thickness of palladium film is from 200 A. to 2000 A. the resistivity ranging from 20 (In to 1 O can be obtained, but when the thickness of the respective films is adjusted, the range of the resistivity can be further increased.

On the other hand, when the intermediate portion of the double-layer film is made into the mixture film of chrome and palladium at an appropriate mixing ration, and when the mixing ratio is gradually changed in the direction of thickness, it is possible to reduce the temperature coefficient or resistivity. The chrome film improves the adhereability to the baseplate, and therefore when other than chrome such as nickel-chrome or chrome alloy, 'or other base metals such as manganese, titanium, beryllium, tantalum or nickel are used, the effectiveness of this invention is not impaired. It is possible to prepare a strongest film when it is prepared under such conditions wherein the temperature of the baseplate is above 200 C. and the degree of vacuum is below 5X10 Torr. In regard to the formation of this film, it is needless to mention here that it can be performed by means of conventional sputtering process, moreover palladium film has excellent wear resistance and antioxidation property which are indispensable factors as the sliding resistance, and at the same time palladium film has such an advantage that it has excellent stability for a high temperature above 200' C., and excellent stability for moisture and overloading.

Referring now to F IG. 3 in which a second embodiment of the invention is disclosed, the chrome-palladium film 2' is deposited in stripe form of increasing lengths from left to right and engaged by a sliding contact 4', the contact having a width slightly greater than the spacing between two adjacent stripes 2. A second resistance film 5 of higher sheet resistance is deposited on the baseplate which may either be deposited under or over the stripes 2'. The form of the second film 5 is also triangular. The sliding contact 4' may be moved within the path between the lines 6 and 7 or within the path between the phantom lines 6' and 7'. In the latter case, the second film 5 should be deposited under the film stripes 2'. It is further possible in the second embodiment to provide a protective film such as a silicon oxide film, on the exposed portions of the second film 5 after the films 2' and 5 have been deposited.

In the embodiment as illustrated in FIG. 3, it will be apparent that the change in the resistance values of the resistor will be stepwise. The width of step changes can be made very small by conventional techniques so that the stepwise changes in resistance values are of no technical disadvantages.

What is claimed is:

l. A variable resistor for measuring instruments comprising a sliding contact,

and insulating plate, and

a thin film resistance of at least two layers including a lower layer which is a tapered resistance layer deposited on said insulating plate and an upper layer deposited on said lower layer, said lower layer being made of a base metal selected from the group consisting of manganese, titanium, beryllium, tantalum, nickel and chrome, said supper layer being made of palladium and being multiple stripes overlaid on said lower layer and extending on said insulating plate, said sliding contact engaging the extending end portions of said stripes.

2. A variable resistor according to claim 1, wherein said lower layerv has a higher sheet resistance than that of said upper layer. 

2. A variable resistor according to claim 1, wherein said lower layer has a higher sheet resistance than that of said upper layer. 